The present invention relates to a magnetoresistance effect device having a spin value structure for utilizing a variation in electrical resistance caused by relationships in variation of both a magnetization direction of a pinned layer and a magnetization direction of a free layer effected by an externally applied magnetic field, and a method of forming the same as well as a magnetoresistance effect sensor and a magnetic recording system.
The magnetoresistance effect sensor or the magnetoresistance effect head are useful for reading data from a magnetic surface at a large linear density. The magnetoresistance effect sensor detects magnetic signals based upon variations in intensity and direction of a detected magnetic flux.
The conventional magnetoresistance effect sensor is operated based upon an anisotropic magnetoresistance effect where one component of a resistance of the reading device varies in proportional to squares of cosine of an angle between a magnetization direction and a defecting current direction flowing through the device. This anisotropic magnetoresistance effect is disclosed in detail in literature IEEE Trans. On Mag. MAG-11, p. 1039, 1975 "D. A. Thomson et al. Memory Storage and Related Application".
In recent years, remarkable magnetoresistance effects have been reported such as a giant magnetoresistance effect and a spin valve effect, wherein the variation in resistance of the magnetic sensor is caused by a spin dependent conductivity of conductive electrons between two magnetic layers sandwiching a non-magnetic intermediate layer and by a spin dependent scattering phenomenon on interfaces thereof.
Those magnetoresistance effect sensors utilizing the giant magnetoresistance effect or the spin valve effect show higher sensitivities or larger variations in resistance than the conventional sensors utilizing the anisotropic magnetoresistance effect. The giant magnetoresistance effect sensor or the spin valve effect sensor utilizes the phenomenon that in-plane resistances of the paired ferromagnetic layers sandwiching the non-magnetic layer vary in proportional to cosine of an angle between the magnetization directions of the paired ferromagnetic layers.
In Japanese laid-open patent publication No. 2-61572, it is disclosed that an antiparallel magnetization causes the big variation in magnetoresistance of the magnetic layered structure. Available materials for the magnetic layered structure are ferromagnetic transition metals and ferromagnetic alloys. Further, it is possible to add an antiferromagnetic layer on one of the paired ferromagnetic layers sandwiching the non-magnetic layer. FeMn is suitable for the antiferromagnetic layer.
In Japanese laid-open patent publication No. 4-358310, it is disclosed that no applied magnetic field to the two thin ferromagnetic layers sandwiching the non-magnetic layer causes that the magnetization directions of the two ferromagnetic layers are perpendicular to each other. A resistance between two non-coupled ferromagnetic layers varies in proportional to cosine of the angle of the magnetization directions of those two layers, so that the magnetoresistance effect sensor shows sensing operation independently from the direction of the current flowing through the sensor.
In Japanese laid-open patent publication No. 6-203340, it is disclosed that two thin ferromagnetic layers are provided which sandwich the non-magnetic thin film and if no external magnetic field is zero, a magnetization direction of an adjacent antiferromagnetic layer is kept in perpendicularly to a magnetization direction of other ferromagnetic layer.
In order to reduce a noise of the magnetoresistance effect sensor, it is important that the variation of the magnetization direction of the free layer due to an externally applied magnetic field is continuous without, however, any hysteresis, for which reason an effective external magnetic field is applied to the free magnetic layer to form a single magnetic domain.
In Japanese laid-open patent publication No. 9-73611, it is disclosed that an antiferromagnetic layer is positioned under a free magnetic layer so that the antiferromagnetic layer is securely contact with the free layer in opposite sides regions defined with predetermined track regions so as to order the magnetization directions of the free layer. In the free layer adhered with the antiferromagnetic layer, an exchange-coupling magnetic field is generated thereby fixing the magnetization direction of the free layer securely in contact with the antiferromagnetic layer. The fixed portion and the continuously varied portion of the free layer are also made into single magnetic domain.
FIG. 1 is a fragmentary cross sectional elevation view illustrative of a lamination structure of a conventional magnetoresistance effect sensor. An externally applied magnetic field to the magnetoresistance effect sensor is directed in an X-direction. This lamination structure is as follows. A bottom gap layer 32 is laminated on a substrate 31. A base layer 33 is laminated on the bottom gap layer 32. A free magnetic layer 34 is laminated on the base layer 33. A non-magnetic layer 35 is also laminated on the free magnetic layer 34. A pinned magnetic layer 36 is also laminated on the non-magnetic layer 35. An antiferromagnetic layer 37 is also laminated on the pinned magnetic layer 36.
For the magnetoresistance effect sensor utilizing the spin valve, it is necessary that the magnetization direction of the pinned layer is fixed by the antiferromagnetic layer. Generally, Fe--Mn, NiO, Ni--Mn, Pt--Mn alloys are available. FeMn and NiO are advantageous in easy formation but disadvantages in low thermal stability due to a low blocking temperature of 200.degree. C.
The antiferromagnetic layer is made of an alloy such as Ni--Mn alloy which has a relatively high blocking temperature of not less than 200.degree. C. whereby the antiferromagnetic layer has a high thermal stability. However, in order to cause the exchange-coupling magnetic field directed in a predetermined direction, it is necessary to carry out a heat treatment in the magnetic field. This heat treatment in the magnetic field provides an influence to the magnetic anisotropy of the free magnetic layer whereby a hysteresis appears on an R-H curve or an electric resistance-magnetic filed curve. As a result, noises are generated in the measurement of the magnetic field.
In the above circumstances, it had been required to develop a novel magnetoresistance effect sensor free from the above problems and a method of forming the same as well as a magnetic recording system.